正斜压模演变所揭示的武汉暴雨过程

对1998年7月21—22日发生在武汉附近的大暴雨过程的大气正、斜压分量演变过程进行了研究，结果表明：大气流场正压分量的演变与此次大暴雨的酝酿、发展和消亡具有内在的联系；正压分量在暴雨区的演变在一定程度上反映高、低空急流耦合形势；正、斜压平均相对模的演变与暴雨生命史相吻合。     

南亚高压季节变化中的正斜压环流转换特征

利用１９５８～１９９７ 年的 Ｎ Ｃ Ｅ Ｐ／ Ｎ Ｃ Ａ Ｒ 再分析资料,采用将大气环流在垂直方向分解为正压和斜压环流两个分量的方法,讨论了南亚高压季节演变中的正斜压环流的转换特征。指出（１）夏季,南亚高压以斜压性为主,其斜压分量约占 ７０ ％ 的比重,冬季以正压性为主,其正压分量约占 ７０ ％ 的比重;（２）由冬季的正压性高压向夏季的斜压性高压的季节演变中,南亚高压是在其斜压分量环流的引导下移动的,即其斜压分量环流的变化超前于其自身的变化;（３）由夏季的斜压性高压向冬季的正压性高压的季节演变则相反,南亚高压是在其正压分量环流的引导下移动的。     

四川盆地暴雨天气过程形成的物理机制分析

对每小时一次的高分辨卫星云图资料分析表明：造成四川盆地暴雨天气过程的中尺度云团是由具有不同天气尺度的形成机制，斜压抬升不是唯一造成盆地暴雨天气的机制。在暴雨天气过程中，各气象要素场相互制约，相互适应，用地转适应的结论和判据，来描述暴雨天气过程中各要素相互适应、制约的方式和条件，为进一步认识、了解盆地暴雨天气形成机制提供了一种新的途径，也为广大预报员提供了一种新的暴雨天气预报思路。由于盆地的特殊地形作用，使对流层中下层的大气状态，有时为准正压结构，有时又为斜压结构．在准正压状态下，盆地暴雨天气的形成机制与热带区积云对流的降雨形成机制相类似。在斜压状态下，盆地暴雨天气的形成机制中、高纬度地区的斜压降雨形成机制，在结构上有着较明显的差异。     

鄂霍茨克海阻高发展过程的正斜压涡度和涡度拟能的演变特征

用正斜压分解法，对1998年发生在鄂霍茨克海的阻高进行涡度和涡度拟以分析，结果发现：在阻高的不同阶段，正压涡度和正压涡度拟能远大于斜压涡度和斜压涡度拟能且在不同的阶段有着不同的演变过程；在阻塞的酝酿阶段正压和斜压涡度和涡度拟能不稳定增长，且向西南传播；在维持阶段，正压和斜压涡度和涡度拟能的增长达到最大值，阻塞形势建立并维持在阻塞区域内；在消亡阶段，正压涡度和涡度拟能与斜压涡度拟能则呈现出不稳定减少，向东南传播，阻塞崩溃，然后又增长。     

一次闽南暖区暴雨的多尺度动力过程

作为气象研究中的一个难点问题,暖区暴雨的动力学一直为学界所关注。基于多尺度子空间变换(MWT)以及基于MWT的局地多尺度能量学分析和正则传输理论,对2018年5月7日的一次闽南暖区暴雨进行研究以了解其多尺度动力过程。首先将原始物理量场重建到三个尺度子空间:背景流子空间、天气尺度子空间和暴雨子空间。重构场上可以很好地看出背景环流尺度的高低空急流,以及暴雨尺度上的垂直环流。以往的研究普遍认为暖区暴雨的动力过程具有弱斜压性这一特征,而就此次事件而言,正压失稳和斜压失稳都起着很关键的作用,暴雨主要落区内既发生了正压失稳,也发生了斜压失稳。研究表明,对流层不同高度上的动力学存在差异,低层主要表现为正压失稳,天气尺度子空间与背景流子空间向暴雨子空间传输的动能相当; 中层主要是混合失稳,除正压失稳外,斜压正则传输也将有效位能从背景流子空间传输到了暴雨子空间,再通过浮力转换将有效位能转为动能,从而维持暴雨在中层的动力过程; 高层则与低层相似,但只存在背景流子空间向暴雨子空间的能量传输。      

2003年一次梅雨大暴雨成因的动力学研究

运用中尺度非静力模式MN5对2003年梅雨期一次大暴雨天气进行数值模拟，在降雨模拟基本正确的基础上分析暴雨发生原因。结果表明：该次梅雨大暴雨属于切变类暴雨，对流层低层有能量锋区、高层有惯性不稳定活动，暴雨区位于低空急流的左前方、高空急流的右前方。暴雨中心物理量要素的时间一高度演变显示：低层正涡度、辐合，高层负涡度、辐散，深厚的上升运动，等相当位温线抬升，湿位涡及其正、斜压分量3者负值加大均有利于降雨加强；暴雨减弱阶段，这些要素一般向相反方向转变。该次大暴雨的直接影响系统具有明显的中尺度时、空特点，大暴雨的发生与高层惯性不稳定和低层对流不稳定有关。     

远距离台风暴雨过程的正/斜压不稳定

利用正／斜压联合不稳定计算方法，分析了由9711号台风引起的远距离台风暴雨(实况及MM4模拟结果)过程中不同时段、不同位置的正／斜压项。结果表明：台风暴雨初始时段的降水主要由台风系统本身正压不稳定扰动引起，随着台风与西风带系统的结合，其南北部出现了2个雨区，均是正／斜压联合不稳定的产物；北部雨区的斜压不稳定较明显，且有随高空急流的非纬向性增强而增强的趋势。     

一次冬季锋面暴风雪天气过程的斜压边界层特征的观测分析

对STORM-FESTIOP17一次冬季锋面暴风雪天气过程的斜压边界层结构演变及特征进行了分析。发现：暖湿空气沿锋面抬升凝结成云，产生降水过程中释放的大量潜热显著增加锋两侧的水平温度差异，产生锋生。与锋生相伴，在锋前产生低空急流和高空急流。当锋生至最强时，锋两侧温差可达20K，锋前低空急流开始减弱，锋后低空急流增强，锋后冷平流开始主导锋两侧的环流系统。该冷平流削弱锋两侧的温度水平梯度，产生锋消作用。对这次锋面斜压对流边界层的湍流特征分析表明：在边界层之上切应力wv明显增大；湍能收支分析表明在边界层之上的风切变产生项很强，即大尺度天气系统有利于斜压对流边界层的发展，边界层内各量充分混合。这次冬季锋面暴风雪天气过程，冷锋前的低空南风急流从墨西哥湾携带来的充足水汽及锋区边界层大气的强斜压性是其产生的关键因子：冷锋过后，大尺度高空急流的作用更有利于对流边界层的充分发展。     

“泰利”台风低压大暴雨过程冷空气与地形的作用

利用常规观测和地面加密资料、自动站资料、闪电定位资料、雷达资料以及NCEP再分析资料,对"泰利"台风低压引发的异常强暴雨事件中纬度冷空气的影响及地形的作用进行了分析.结果表明:在华西地区大陆高压与副热带高压形成对峙的背景条件下,中纬度冷空气从850 hPa以下低层不断侵入台风低压的北部,增强了其北侧的东北气流,它与来自东部海面上的东风气流在台风低压北部形成汇合;随着中纬度冷空气主体进入江淮地区,台风低压的正压结构缓慢向东暖西冷的斜压结构转换,总能量的水平分布也由螺旋型涡旋逐渐演变为NE-SW向的椭圆型结构,斜压能量的补充有利于台风低压长时间维持;湿位涡正压项的分析表明,随着台风低压进入消亡期,其上空大气变为对流不稳定.行星边界层能量锋区的加强,触发了β中尺度对流系统,导致在台风低压消亡时出现强雷暴天气;强降水主要分布在大别山东麓和九岭山脉迎风坡上,地形对偏东气流的抬升作用有利于暴雨的增幅.     

亚洲夏季风结构和变动与大气运动的斜压和正压特征:斜压模分析

通过定义流场的斜压性度量参量，利用观测资料，对大气运动的斜压特征量与夏季风变动的联系进行了探讨。结果表明：夏季风流场具有较强的斜压性；纬向气流的斜压强弱的时间变动与夏季风进退相吻合；强斜压区的范围可反映夏季风活动的基本范围。经向斜压运动强弱的水平分布及时间－经度剖面上斜压运动动能的纬向传播都与亚洲季风体系中季风子系统有关     

Nonlinearity and Finite-Time Instability in a T21L3 Quasigeostrophic Model

In this paper,a nonlinear optimization method is used to explore the finite-time instability of the atmospheric circulation with a three-level quasigeostrophic model under the framework of the conditional nonlinear optimal perturbation (CNOP).As a natural generalization of linear singular vector (SV),CNOP is defined as an initial perturbation that makes the cost function the maximum at a prescribed forecast time under certain physical constraint conditions.Special attentions are paid to the different structures and energy evolutions of the optimal perturbations.The results show that the most instable region of the global atmospheric circulation lies in the midlatitude Eurasian continent.More specially,SV and CNOP in the total energy norm with an optimization time of 2 days both present localness:they are mainly located in the midlatitude Asian continent and its east coast.With extension of the optimization time,SVs are more upstream and less localized in the zonal direction,and CNOPs differ essentially from SVs with broader zonal and meridional coverages; as a result,CNOPs acquire larger kinetic and available potential energy amplifications than SVs in the nonlinear model at the corresponding optimization time.For the climatological wintertime flow,it is seen that the baroclinic terms remain small over the entire time evolution,and the energy production comes essentially from the eddy kinetic energy,which is induced by the horizontal shear of the basic flow.In addition,the effects of SVs and CNOPs on the Eurasian atmospheric circulation are explored.The results show that the weather systems over the Eurasian continent in the perturbed fields by CNOPs are stronger than those by SVs at the optimization time.This reveals that the CNOP method is better in evaluating the instability of the atmospheric circulation while the SV method underestimates the possibility of extreme weather events.     

BAROTROPIC AND BAROCLINIC PATTERNS OF ATMOSPHERIC CIRCULATIONS RELATED TO MONSOON TYPES

In the context of 1982—1994 NCEP/NCAR wind at 12-level isobaric surfaces on a global basiscalculation is made of the barotropic(mass-weighed vertical mean)and baroclinic components(difference between the actual wind at each level and barotropic component)of atmospheric flowfields,followed by dealing with the distribution features of barotropic and baroelinie patternsglobally in winter and summer,alongside with the classification of global monsoons according tothe surface barotropic/baroclinic patterns.Evidence suggests that the seasonal variation of bothcomponents will lead to the reversal of a prevailing wind between winter and summer,thus causinga related monsoon:the baroclinie flow pattern is indicative of a thermal circulation driven byatmospheric inhomogeneous heating chiefly from land-sea thermal contrast whilst the barotropiccounterpart represents the result mainly from dynamic effects,which is helpful to theunderstanding of monsoon nature.And further study shows that the classical monsoon regions intropical Asia,Africa and South America fall into a baroclinic category,those in the bi-hemispheriesubtropical Pacific into a barotropic type and the East Asian subtropical monsoon generated underthe joint action of both the patterns falls into a mixed category.     

Nonlinearity and finite-time instability in a T21L3 quasigeostrophic model

In this paper, a nonlinear optimization method is used to explore the finite-time instability of the atmospheric circulation with a three-level quasigeostrophic model under the framework of the conditional nonlinear optimal perturbation (CNOP). As a natural generalization of linear singular vector (SV), CNOP is defined as an initial perturbation that makes the cost function the maximum at a prescribed forecast time under certain physical constraint conditions. Special attentions are paid to the different structures and energy evolutions of the optimal perturbations.     

阻塞过程中正斜压涡度拟能相互转换机制的重要性

使用正斜压涡度拟能方程对一次乌拉尔山阻塞过程的研究表明，虽然正、斜压涡度拟能向阻塞区内的净输送、阻塞区域内正斜压涡度拟能的净生成以及β效应是阻塞环流建立、维持和崩溃的基本能源，但正斜压涡度拟能相互转换机制则是阻塞过程得以形成的根本原因。如果没有正斜压涡度拟能相互转化机制，则阻塞环流不但不能形成，反而使大气的斜压性不断增强，正压性不断减弱。     

BAROTROPIC AND BAROCLINIC PATTERNS OF ATMOSPHERIC CIRCULATIONS RELATED TO MONSOON TYPES*

In the context of 1982-1994 NCEP/NCAR wind at 12-level isobaric surfaces on a global basis calculation is made of the barotropic(mass-weighed vertical mean) and baroclinic components(difference between the actual wind at each level and barotropic component) of atmospheric flow fields,followed by dealing with the distribution features of barotropic and baroelinie patterns globally in winter and summer,alongside with the classification of global monsoons according to the surface barotropic/baroclinic patterns.Evidence suggests that the seasonal variation of both components will lead to the reversal of a prevailing wind between winter and summer,thus causing a related monsoon:the baroclinie flow pattern is indicative of a thermal circulation driven by atmospheric inhomogeneous heating chiefly from land-sea thermal contrast whilst the barotropic counterpart represents the result mainly from dynamic effects,which is helpful to the understanding of monsoon nature.And further study shows that the classical monsoon regions in tropical Asia,Africa and South America fall into a baroclinic category,those in the bi-hemispheric subtropical Pacific into a barotropic type and the East Asian subtropical monsoon generated underthe joint action of both the patterns falls into a mixed category.     

一个正压和斜压不稳定的充要条件

提出一个新的李雅普诺夫函数，首次得到了正压和斜压不稳定的充要条件，大大改善了热知的Ｒａｙｌｅｉｇｈ－郭晓岚定理和Ｆｊｏｒｔｏｆｔ定理，解决了Ｒａｙｌｅｉｇｈ（１８８０）提出的无粘切变流正压稳定性问题。     

亚洲季风变动与大气正压/斜压运动动能变化的气候特征

使用ＮＣＥＰ／ＮＣＡＲ４０年（１９５８～１９９７年）月平均再分析资料,通过动力学论断研究了大气斜压／正压运动动能的变化及其相互转换,分析了亚洲季风变动与这两种动能变化的联系。指出：季风区大气运动动能的组成和变化具有独特的特征。冬季风时期大气斜压运动动能与正压运动动能具有正相关线性关系,斜压运动能向正压运动动能转换;春、秋季无论是东亚还是印度季风区斜压运动动能与正压运动动能之间转换都处于极小值,只是     

ANALYSIS OF THE INTER-TRANSFOMATION OF EQUIVALENT BAROTROPIC AND BAROCLINIC ROSSBY WAVES

By using the low-spectral model simplified from quasi-geostrophic approximation two-levelmodel,we obtained the result that the equivalent barotropic state is an equilibrium state of theatmosphere in that model,and discussed the conditions needed for existing the Rossby wavepossessing the equivalent barotropic structure.And then we derived the oscillation equation reflectingthe phase change of Rossby wave between higher and lower levels from the basic state of equivalentbarotropic stationary Rossby wave,indicating the relations between the change of difference of phaseat higher and lower levels and the disturbance of vertical shear,the amplitude disturbance of the partof waves of stream function and thermal wind stream function on the average level (A′ and B′).It isconcluded that the inter-transformation exists between Rossby waves possessing the equivalentbarotropic and baroclinic structure.